Tube Current - Exposure Time Product (mAs)

80 kV, 16mAs, S = 225

The image above shows a computed radiography image of a pelvis phantom that was generated using 80 kV and 16 mAs, and employing a scatter removal grid. This is a typical radiographic technique, and results in a skin dose of 1.6 mGy. For this technique, the S number was ~220, which corresponds to a radiation intensity incident on the imaging plate of ~9 mGy, showing that only 0.6% of the radiation intensity incident on the patient reaches the imaging plate.

The small ROI shows the magnitude of random fluctuations (noise or mottle), as well as the line profile shown through the image. The five images below generated at progressively lower techniques, with the mAs halved for each progressive scan. Every time the mAs is reduced by a factor of two, the entrance skin dose is halved, the S number associated with the image is doubled, and the appearance of noise or mottle is increased by a factor of 2^0.5.

80 kV, 8 mAs, S = 459

The skin dose in this image is one half the skin dose of the case shown above (0.8 mGy), and the receptor dose is also halved (~4.5 mGy). Note that the mottle, as shown by the ROI and profile data above, have increased. The increase in mottle is approximately equal to 2^0.5, since the number of photons (proportional to the mAs) has been halved.

80 kV, 4mAs, S = 836

The skin dose in this image is one half the skin dose of the case shown above (0.4 mGy), and the receptor dose is also halved (~2.3 mGy). Note that the mottle, as shown by the ROI and profile data above, has increased. The increase in mottle is approximately equal to 2^0.5, since the number of photons (proportional to the mAs) has been halved.

80 kV, 2mAs, S = 1630

The skin dose in this image is one half the skin dose of the case shown above (i.e., 0.2 mGy), and the receptor dose is also halved (~1.2 mGy). Note that the mottle, as shown by the ROI and profile data above, has again increased. The increase in mottle is approximately equal to 2^0.5, since the number of photons (proportional to the mAs) has been halved.

Pelvis 6, 80 kV, 1mAs, S = 3648

The skin dose in this image is one half the skin dose of the case shown above (i.e., 0.1mGy), and the receptor dose is also halved (~0.55 mGy). Note that the mottle, as shown by the ROI and profile data above, have again increased. The increase in mottle is approximately equal to 2^0.5, since the number of photons (proportional to the mAs) has been halved.

Pelvis 7, 80 kV, 0.5 mAs, S = 5522

The skin dose in this image is one half the skin dose of the case shown above (i.e., 0.0.5mGy), and the receptor dose is also halved (~0.36 mGy). Note that the mottle, as shown by the ROI and profile data above, have again increased. The increase in mottle is approximately equal to 2^0.5, since the number of photons (proportional to the mAs) has been halved.